Traditional liposomes primarily consist of phospholipids and cholesterol: Phospholipids have a hydrophilic head and two hydrophobic tails. The head is composed of a phosphate backbone esterified with water-soluble molecules like choline or serine, making it water-soluble. The parallel tails are fatty acid chains, each containing 10–24 carbon atoms and 0–6 double bonds, which are insoluble in water. Cholesterol is a neutral lipid with a higher affinity for lipids than for water. Cholesterol itself does not form lipid bilayers, but it can intercalate into the phospholipid membrane, with its hydroxyl group facing the hydrophilic surface and its aliphatic chain oriented parallel to the hydrocarbon chains in the center of the phospholipid bilayer.
Liposomes, due to their structural similarity to cell membranes, can enhance the penetration of active ingredients into the skin, improve the delivery of active substances into the stratum corneum or the epidermal lipids, increase the accumulation of active ingredients in the skin, thereby enhancing bioavailability, reducing adverse effects, and providing a sustained release effect.
In 1986, Dior launched the “capture” line of liposome-based cosmetics, pioneering the use of liposomes in cosmetics.
Mechanisms of transdermal delivery by liposomes:
- Penetration Mechanism: Intact liposomes can pass through the stratum corneum and penetrate deeper into the skin, potentially reaching the bloodstream.
- Hydration Mechanism: Liposomes can hydrate the stratum corneum, enhancing hydration, expanding the gaps between keratinocytes, and disrupting the alignment of hydrophobic tails in the lipid bilayer. As a result, lipid-soluble drugs can enter the intercellular spaces through diffusion and capillary action.
- Fusion Mechanism: The phospholipids in liposomes can interact with the lipids in the stratum corneum, causing changes in the lipid composition and structure of the stratum corneum. This leads to the formation of flat, granular structures, through which the active ingredients encapsulated in liposomes can enter the skin.
Compared to traditional cosmetics, liposome-based cosmetics offer several advantages:
- Protective Effect: Enhances the stability of active ingredients both inside and outside the body and reduces skin irritation.
- Amphiphilic Properties: Can deliver both water-soluble and lipid-soluble active substances to the deeper layers of the skin.
- Sustained Release: Provides a slow release of active ingredients, extending their action time on the skin.
- Moisturizing Effect: Keeps the skin hydrated, with the lipids penetrating the skin to prevent the loss of internal moisture, thus moisturizing and softening the skin.
- Skincare Benefits: Reduces the deposition of excess fats and toxins on the skin, hydrates keratinized tissues, and achieves skincare objectives.
In summary, liposomes are an excellent type of active ingredient carrier with high biocompatibility, biodegradability, non-toxicity, non-immunogenicity, low side effects, targeted delivery, and controlled release properties. They have been widely used in the cosmetics industry for both water-soluble and oil-soluble ingredients, such as ceramide liposomes, astaxanthin liposomes, centella liposomes, acetyl hexapeptide-8 liposomes, and retinol liposomes.
